In recent times driver workload, and its impact upon driver performance, has attracted increasing interest. Driver workload is representative of the demands placed on a driver while driving, and is based on a primary contribution in respect of the main task of driving, and a secondary contribution in respect of peripheral activities, for example use of in-vehicle systems, e.g. navigation devices such as personal navigation devices (PNDs) or integrated navigation devices, or Advanced Driver Assistance Systems (ADAS). Driver workload as used herein may also be referred to as “driver mental workload”, and references to “driver workload” may be replaced with references to “driver mental workload”.
A driver's mental capacity must be sufficient to attend to the primary task of driving and any peripheral activities. Any increase in driver workload required by in-vehicle systems will take up mental capacity, and will reduce the mental capacity available to attend to the task of driving, potentially compromising safety. The task of driving may require differing amounts of mental capacity under different circumstances, e.g. weather, lighting, etc, and depending upon the individual driver, e.g. age, experience, particular difficulties, etc. It is important therefore to balance the level of driver workload associated with in-vehicle systems for different circumstances and for different drivers, taking into account the mental capacity required to perform the main function of driving.
Understanding driver workload is therefore important in designing in-vehicle systems, to ensure that the systems support the driver, and avoid overburdening the driver. Systems, and in particular their communication with a driver, may be adapted depending upon a predicted or detected workload for a given set of circumstances. For example, certain functions may be disabled to allow the driver to focus on the task of driving, or a display or other output of a system may be altered to control the amount of information presented to the driver at any time depending upon the determined workload.
Various techniques have been proposed for measuring or otherwise determining driver workload. This may involve sensing of certain parameters indicative of workload, including parameters indicative of driving style, behavioural and psychological parameters. Driver workload levels may be assessed by reference to detected parameters relating to the individual driver, and may take into account historic behaviour of the driver. A driver profile may be generated for a given driver indicative of workload when performing different activities. For example, various known methods of assessing driver workload, and adjusting the operation of in-vehicle systems in dependence on the assessed workload level, are described in US 2006/0293799 A1, US 2007/0124027 A1, US 2005/0234617 A1 and US 2006/0015219 A1.
The Applicant's co-pending application, published as WO 2008/004857 A1, and entitled “Navigation Device with Adaptive Navigation Instructions”, discloses a navigation device in which navigation instructions are adapted according to an individual driver profile, in order to better conform to the drivers preferences and to contribute to safer behaviour. The driver profile may be based on parameters reflecting driver preferences or habits. The driver profile parameters may include parameters derived from driver input information or preferences, and also parameters based on detected behaviour of a driver. For example, the ability of a driver to follow route navigation instructions under different conditions e.g. different times of day, week or year, weather or lighting conditions etc may be detected, and used in providing the profile. The navigation instructions output by the device are adapted based upon the profile data using a “profile-to-instruction translator”. For example, the density or detail of instructions may be adjusted, mode of output, e.g. whether visual or audible, etc. The entire contents of WO 2008/004857 A1 is incorporated herein by reference.
Another co-pending application of the Applicant, published as WO 2009/143903 A1, and entitled “Navigation Apparatus and Method that Adapt to Driver's Workload”, discloses a navigation apparatus in which the workload of the driver is determined and used to provide or alter communication with the driver dependent upon the determined workload of a driver at a given time. The workload parameter may be based on various factors including sensed physiological parameters, psychological parameters, environmental factors, external factors and dynamic factors, and may be based in part upon driver input data. The drivers behaviour may be assessed by reference to that of other drivers. For example, where the drivers speed is found to be less than or greater than an average speed of other traffic surrounding the driver at that time, or less than or greater than a historical average speed for the relevant section of road, this may be indicative of fatigue or stress respectively. An individual historical driver profile may be determined which can be used in the calculation of driver workload. The driver profile may be updated and changes in the profile used as a measure of driver workload. The workload information may be used in various ways to control communication with the driver e.g. adjusting frequency or mode of instructions, adjusting display of instructions. The application also discloses that historical driver profile data may be used to provide a data map, indicative of a variation in driver workload throughout a road network. The entire contents of WO 2009/143903 A1 is also incorporated herein by reference.
Although considerable effort has been directed to the determining of driver workload, and its use in controlling the operation of in-vehicle systems (and devices that can be removably mounted within vehicles), the Applicant has realised that there remains a need for improved methods and systems for determining the workload of an individual driver.